Fluid Mechanics Problem: Calculate Force on Lower Plate

In summary, the conversation discusses solving a fluid mechanics problem involving laminar flow with a given velocity distribution equation and plate distance. It includes calculating shear stress and net force on a plate using the velocity gradient and viscosity. The solution results in a net force of -22.28 N/m^2 in the negative x-direction.
  • #1
JSBeckton
228
0
I'm struggling with a fluid mechanics problem:
The velocity distribution for laminar flow is given by
U/Umax = 1 -[2y/h]^2
h = dist between plates. origin is midway between plates, Consider the flow of water at 15 degrees C with max speed .005 m/s and h=1mm. Calculate the force on a 1m^2 section of the lower plate and give its direction.

Viscosity at 15 degrees C = 1.114x10^-3
What direction should I be going in here? Do I need to use the velocity equation to solve for U and then find the force with a different equation?
Thanks for any help.
 
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  • #2
Assuming the flow is fully developed which it seems to be judging by the 1-D equation you gave the shear stress at the wall is simply

tau = mu du/dy, (evaluated a y = -0.5*h)

where mu is the viscosity.

du/dy = Umax*(8y/h^2), which becomes -8/2h= Umax*(-4/h) = 0.005*(-4/0.001) = -20

times the viscosity this becomes,

1.114*10^-3*-20 = -22.28 N/m^2

Since the area is 1 m^2 the net force of the plate on the fluid is 22.28 [N] in the negative x-direction

I hope this was of any help. I am pretty sure you have to use the velocity gradient at the bottom location. I am tired so I may have made a mistake but the principle should be pretty clear

Jaap
 
Last edited:
  • #3
Thanks, it helped.
 

What is fluid mechanics?

Fluid mechanics is a branch of physics that deals with the study of how fluids (liquids and gases) behave under different conditions, such as when they are in motion or at rest. It involves the study of properties such as pressure, velocity, and density, and how they are related to each other.

What is the purpose of calculating force on a lower plate in a fluid mechanics problem?

The purpose of calculating the force on a lower plate in a fluid mechanics problem is to understand how the fluid is exerting pressure on the plate and how the plate is reacting to this pressure. This information is important in designing and analyzing various systems and structures that involve fluid flow, such as pipes, pumps, and turbines.

How do you calculate the force on a lower plate in a fluid mechanics problem?

The force on a lower plate can be calculated by using the equation F = P * A, where F is the force, P is the pressure exerted by the fluid, and A is the area of the plate. The pressure can be calculated using the Bernoulli's equation or by using the concept of hydrostatic pressure, depending on the specific problem.

What factors affect the force on a lower plate in a fluid mechanics problem?

The force on a lower plate can be affected by several factors, including the density and velocity of the fluid, the shape and size of the plate, and the angle at which the fluid is hitting the plate. These factors can impact the pressure exerted on the plate, which in turn affects the force.

How can the force on a lower plate be used in real-world applications?

The calculation of force on a lower plate is used in various real-world applications, such as designing and analyzing the performance of hydraulic systems, aircraft wings, and submarine propellers. It is also used in the design of dams and other structures that involve the flow of water.

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